KIRSTEN GRIESHABER, DANIEL NIEMANN BERLIN — A former Ukrainian army officer is going on trial in Germany this week over undersea explosions that damaged the Nord Stream gas pipelines between Russia and Germany four years ago in one of the biggest acts of sabotage in Europe since the Second World War. The suspect faces charges of causing an explosion, damaging property, disrupting public service and being an “accomplice to war crimes” by attacking civilian infrastructure, according to prosecutors .

The attack laid bare Europe’s dependence on Russian energy but also raised sensitive questions about Ukraine and its Western allies.

While international observers initially blamed Moscow, there are now increasing suggestions that Ukrainian state security agencies may have been involved — even though Ukraine counts Germany as one of its closest allies.

According to German privacy rules, the suspect will be identified in court only as Serhii K., although he was publicly named as Serhii Kuznietsov in extradition proceedings in Italy .

Here’s what we know about the alleged ringleader of the attack and one of the most politically charged court cases of wartime sabotage that will be heard at the Hanseatic Higher Regional Court in Hamburg starting this Wednesday.

The explosions on Sept. 26, 2022, damaged pipelines that were built to carry Russian natural gas to Germany under the Baltic Sea. At the time, European countries were moving to wean themselves off Russian energy sources, following the Kremlin’s full-scale invasion of Ukraine in February 2022 .

Prosecutors say the aim of the plot was to permanently disrupt gas deliveries and prevent Russia from using the revenues to finance its military operations.

The defendant and others allegedly used a yacht that set off from the German port of Rostock.

It had been hired from a German company using forged IDs and with the help of intermediaries.

The explosions ruptured the Nord Stream 1 pipeline, which was Russia’s main natural gas supply route to Germany until Moscow cut off supplies in August 2022. They also damaged Nord Stream 2, which never entered service because Germany suspended its certification process shortly before Russia’s invasion of Ukraine.

The suspect allegedly organized and carried out the detonation of at least four bombs between 14 and 27 kilograms (around 31 to 62 pounds) at a depth of 70 to 80 meters (230 feet to 263 feet) near the Danish island of Bornholm. He was detained in August in an Italian village, where officers raided a bungalow where he was staying with his family.

Police said he surrendered without resistance.

He was extradited to Germany in November. A second suspect was arrested on a European warrant in the northern Croatian town of Pula in August. He has applied for asylum in Croatia to fight his extradition to Germany.

The pipelines were long a target of criticism by the U.S. and some of its allies, which warned that they increased dependence on Russian gas. Russian officials, however, have claimed that U.S. and British intelligence agencies were involved in staging the explosions, which Moscow declared “an act of international terrorism,” and have launched their own investigation.

Russia has also accused NATO of involvement in the attack, while several Western countries initially blamed Russia.

More recently, the Kremlin has expressed hope that those who orchestrated the explosions will be held accountable.

Asked what Moscow expects from the trial, Kremlin spokesperson Dmitry Peskov said Monday that “we expect objectivity.”“We expect … that both the perpetrators and those who ordered it will be named. That would be very important. I think no one doubts who it really is,” Peskov said.

Ukrainian President Volodymyr Zelenskyy has denied allegations that his country was involved in the pipeline blasts. He also told reporters in August that Ukraine’s prosecutors and Foreign Ministry were already cooperating with partners and that Kyiv was “absolutely open to joint steps on the investigation,” stressing the importance of keeping Europe’s trust.

Nonetheless, “all the evidence points very clearly to the fact that Ukraine blew up the Nord Stream pipelines, not the Russians, whom they initially tried to pin the blame on,” says Joachim Weber, a security expert at the Center for Advanced Security, Strategic and Integration Studies at the University of Bonn.

“This is, of course, highly explosive politically, because, as is well known, Germany is one of Ukraine’s closest allies, supporting the country on a massive scale with huge sums of money and also by taking on considerable political risks,” Weber said.

However, the German government has so far refrained from comment on the upcoming trial, pointing out that no verdict has yet been reached and the case is in the hands of the independent judiciary.

Even if it were proven in the course of the trial that Ukrainian government agencies were somehow involved in the sabotage act, that would likely have few consequences for Germany’s relationship with Ukraine, “because we naturally want Ukraine to survive,” not least as a buffer against Russia, said Weber.

“In that respect — even if it sounds cynical to some — Ukraine also serves a purpose for us, and it is in our interest to preserve it,” he said.

The outcome of the trial is unlikely to have major repercussions on German-Ukrainian relations, he argued.

“In short, I don’t see us going through some kind of list of punishments against Ukraine right now,” Weber said. “But we should take this as a warning, so to speak, to view things realistically.”

Niemann reported from Bonn, Germany. AP writers Hanna Arhirova in Kyiv, Ukraine and Jovana Gec in Belgrade, Serbia contributed reporting.